Pressure vessels (PVs) are important for many domestic and industrial applications, such as hot-water storage systems, mining operations, liquefied gas storage systems, nuclear reactor vessels and distillation towers, among others. For proper performance and continued safety of those using the system, it's important to implement stringent measures to prevent processes that damage these vessels.
Corrosion is one process, and it can occur as a result of various factors in the internal and external environment around PVs. If discovered early, corrosion damage can be treated and the vessels be restored to working condition, but prevention is always better than cure. Understanding triggers of corrosion in PVs is vital to preventing it, and these are highlighted below.
Causes of corrosion
The internal environment
Inside a PV, corrosion can occur as a result of many factors. Some of these include prolonged exposure to dissolved oxygen and chelants and accumulation of copper deposits. Chelants are specific chemicals added inside PVs to maintain solubility of minerals in the vessel. However, these chelants can cause corrosion if they interact with salts. Dissolved and non-dissolved oxygen provides perfect conditions for corrosion since PVs are usually made of steel, while copper deposits can trigger electrolysis which causes corrosion.
The external environment
Outside of a PV, corrosion can occur as a result of non-uniform stresses on particular points of the high pressure system. Coupled with exposure to high temperatures, these stresses can expose weak/vulnerable areas such as those affected by transgranular cracking or caustic embrittlement. Transgranular cracking is triggered by hot gas accumulation around the vessel, while caustic embrittlement comes as a result of exposure to sodium hydroxide, a caustic alkali. Both processes can cause cracking, leading to leaking and/or loose tubes.
Prevention of corrosion
Regular inspection
Proper maintenance of PVs is one of the best ways to reduce PV corrosion risks, especially once they are filled. PVs typically contain pressurized materials and toxic gases, which could result in environmental contamination and even loss of life should they leak out from places affected by corrosion.
Regular inspection by qualified professionals and pressure vessel registration is a requirement by law, but it also ensures that potential problem areas are identified and fixed before damage can result. Even though corrosion damage is treatable, treatment is much more expensive and difficult than prevention and will shorten the lifespan of your vessels.
Preventive maintenance
In addition, industries with PVs should implement scheduled preventive maintenance programs which outline deterioration issues and treatment procedures. Practically, this means that it isn't enough to discover a worn seal then record it for the person in the next shift to fix; it must be fixed immediately it is noticed. Safety risks can only be prevented by replacing potentially weak points in a timely fashion. Finally, PV associated frameworks should be fitted with safety measures and safety protocols be followed to the letter. This includes putting on protective gear, and installing safety rails and ladders among others.
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